1. Field of the Invention
The present invention relates to a method for halogen exchange reaction and, more particularly, to a method for producing 1,4-bis(difluoromethyl)tetrafluorobenzene, which is simple and highly-yielding.
2. Description of Related Art
As techniques of integrated circuits have progressed, semiconductor components are designed towards miniaturization and high speed. In order to dispose more and more components on a finite area of a chip, i.e. to upgrade integration of components on a chip, two or more metal interconnection layers are required to be transmittals for signals between components and the external environment, and accordingly there can be provided sufficient area to make interconnects. Therefore, transmittal speed between internal components and the external environment is determined by interconnect capacitance, i.e. RC delay, rather than switching speed of gates. Since using low dielectric constant materials can alleviate RC delay, much research is currently focusing on development of low dielectric constant materials.
Organic polymers containing fluorine now are widely used due to their low dielectric constant and easy to use in processes of current semiconductor techniques. In general, methods for decreasing dielectric constant of organic materials can be classified into physical and chemical methods. In the case of physical methods, the thickness of the thin film is enlarged to reduce dielectric constant. With regard to chemical methods, there are two common ways as follows. First is to raise the amount of fluorine in a molecule: fluorine atoms are introduced into a monomer of the molecule by chemical methods to raise the amount of fluorine therein, thereby increasing atomic or molecular packing density. Second is to increase free volume: atoms or molecular groups having large volume are introduced into polymer films to lower atomic or molecular packing density, resulting in a decrease in dielectric constant.
Since polymers of aromatic compounds containing fluorine generally have advantageous properties such as transparency, thermal and chemical resistance, water repellent, low dielectric constant, low reflectivity and so on, Bailey et al. (J. Fluor. Chem., 1987, 37: 1-14) discloses a method for preparing aromatic compounds having a benzene ring substituted with four fluorine atoms and a side chain also substituted with fluorine. Specifically, in this method, the benzene ring and the side chains of p-xylene are fluorinated by complex metal fluoride. The fluorination is performed as the reaction (I) listed following.
However, this method itself has shortcomings listed as follows: (1) complex metal fluorides such as CsF and CoF3 are very expensive; (2) fluorination on the benzene ring and the side chain hydrogen needs to be performed under the condition of the high temperature (360° C.); (3) due to carrying out in a gas phase fluorination reaction, it needs complex equipment; and (4) varieties of excess byproducts result in difficulty of purification.
Because techniques for manufacturing integrated circuits have been upgraded progressively, there is a demand for dielectric materials to have lower and lower dielectric constants for industries, and their costs are required to be reasonable so as to enhance the competitiveness of industries. Hence, how to provide a method, which has simple reactions and can be used for quantity production, of preparing a monomer containing fluorine of a polymer with low dielectric constant has become a current issue waiting for resolution. The present invention provides a method of preparing an important precursor, 1,4-bis(difluoromethyl)tetrafluorobenzene, of 1,4-bis-(bromodifluoromethyl)tetrafluorobenzene to achieve the foregoing purposes of having simple reactions and quantity production.